This name is not my style. But if a name like Avery or Austin can be a girl's name, why not Sullivan? When it comes to androgynous names I don't think there's many rules. I don't think it's very flattering on a girl, but again it's not my style and I don't really like super androgynous names in the first place. But if that's your style, why not?

The whole last-names-as-first-names-on-girls thing just annoys me. There are so many girls' names out there; why name them surnames/boys' names? I think it would be ok as a middle if you were honoring a Sullivan, but aside from that, no.